1. Field of the Invention
The present invention relates to a sealing material, and more specifically, it relates to a sealing material suitable for filling up a clearance between a coated steel plate and a component forming a gasket in a flange part of a trunk lid of an automobile or the like.
2. Description of the Prior Art
A sealing material, which is employed in various fields, fills up a clearance between a coated steel plate and a component forming a gasket in a flange part of a trunk lid of an automobile, for example, for sealing and rust prevention. FIG. 1 is a sectional view showing such a flange part A hollow-sealing member 2 for sealing a trunk room when closing a trunk lid is integrally formed with a gasket 4. A sealing member 6 fills an inner part of the gasket 4, which is engaged with a coated steel plate 8 of the trunk lid for dipping the forward end of the coated steel plate 8 into the sealing material 6.
The material for the gasket 4 has been mainly prepared from a rubber material such as PVC (polyvinyl chloride), SBR (styrene-butadiene rubber), NR (natural rubber) or CR (chloroprene rubber). Furthemore, EPDM (ethylene-propylene rubber) is generally employed particularly in recent years, while thermoplastic elastomer such as TPO (olefinic elastomer) is regarded as a promising advanced material.
The coated steel plate 8 of the flange part is formed by a baked coated steel plate of melamine, acrylic or melamine acrylic.
The sealing material 6 for filling up the inner part of the gasket 4 must have the following characteristics:
(1) To hold viscosity over a long period after filling up the inner part of the gasket 4; PA1 (2) to have less swelling action of the gasket 4 of synthetic resin or synthetic rubber, PA1 (3) to minimize contamination or swelling of the coated steel plate 8; PA1 (4) to have less self-volume shrinkage factor; PA1 (5) to have no self-foaming or swelling, PA1 (6) to be readily engaged with the coated steel plate 8 of the flange part after filling the inner part of the gasket 4; and PA1 (7) not to ooze out from the gasket 4.
A sealing material for filling a clearance between a coated steel plate and a part forming a gasket in a flange part of an automobile is mainly prepared from a polybutene material or a butyl rubber material. The polybutene sealing material is a composite prepared by blending an adhesive component of polybutene resin with an oil extender which includes a plasticizer, process oil, polypropylene glycol having a hydroxyl group on one or each end and a solvent, and a powder filler.
The butyl rubber sealing material is prepared by dissolving butyl rubber in process oil or a solvent and blending the same with the aforementioned oil extender and a powder filler.
However, when employing the polybutene sealing material, the polybutene itself, and the plasticizer, the process oil, or the solvent which are contained in the oil extender, disadvantageously swells the gasket Furthermore, the plasticizer or the process oil, which are contained in the oil extender, erodes the coated steel plate to swell or contaminate the same. In addition, the sealing material remarkably shrinks due to evaporation of the oil extender or the solvent.
On the other hand, in the butyl rubber sealing material,, the viscosity of the composite increases due to volatilization of the solvent in addition to the aforementioned action of swelling the gasket Thus, the sealing material cannot be readily engaged with the coated steel plate of the flange part Furthermore, the sealing material disadvantageously shrinks due to volatilization of the oil extender or the solvent.